strtod, strtof, strtold - convert ASCII string to floating-point number
double strtod(const char *nptr, char
float strtof(const char *nptr, char
long double strtold(const char *nptr, char
Feature Test Macro Requirements for glibc (see feature_test_macros(7)
_POSIX_C_SOURCE >= 200112L
(), and strtold
() functions convert the
initial portion of the string pointed to by nptr
, and long double
The expected form of the (initial portion of the) string is optional leading
white space as recognized by isspace(3)
, an optional plus ('+') or
minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal
number, or (iii) an infinity, or (iv) a NAN (not-a-number).
A decimal number
consists of a nonempty sequence of decimal digits
possibly containing a radix character (decimal point, locale-dependent,
usually '.'), optionally followed by a decimal exponent. A decimal exponent
consists of an 'E' or 'e', followed by an optional plus or minus sign,
followed by a nonempty sequence of decimal digits, and indicates
multiplication by a power of 10.
A hexadecimal number
consists of a "0x" or "0X"
followed by a nonempty sequence of hexadecimal digits possibly containing a
radix character, optionally followed by a binary exponent. A binary exponent
consists of a 'P' or 'p', followed by an optional plus or minus sign, followed
by a nonempty sequence of decimal digits, and indicates multiplication by a
power of 2. At least one of radix character and binary exponent must be
is either "INF" or "INFINITY",
is "NAN" (disregarding case) optionally followed by a
, where n-char-sequence
specifies in an
implementation-dependent way the type of NAN (see NOTES).
These functions return the converted value, if any.
is not NULL, a pointer to the character after the last
character used in the conversion is stored in the location referenced by
If no conversion is performed, zero is returned and (unless endptr
null) the value of nptr
is stored in the location referenced by
If the correct value would cause overflow, plus or minus HUGE_VAL
) is returned (according to the sign of the
value), and ERANGE
is stored in errno
. If the correct value
would cause underflow, zero is returned and ERANGE
is stored in
- Overflow or underflow occurred.
For an explanation of the terms used in this section, see attributes(7)
|strtod (), strtof (), strtold ()
POSIX.1-2001, POSIX.1-2008, C99.
() was also described in C89.
Since 0 can legitimately be returned on both success and failure, the calling
program should set errno
to 0 before the call, and then determine if an
error occurred by checking whether errno
has a nonzero value after the
In the glibc implementation, the n-char-sequence
that optionally follows
"NAN" is interpreted as an integer number (with an optional '0' or
'0x' prefix to select base 8 or 16) that is to be placed in the mantissa
component of the returned value.
See the example on the strtol(3)
manual page; the use of the functions
described in this manual page is similar.
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